1. Field of the Invention
The present invention relates to a method for controlling the position of a web moving along a given path and an apparatus for use in such method and, in particular, to a method and an apparatus for correcting the meandering of a thin, moving strip (which is hereinafter referred to as a web) such as paper, a plastic film, cloth, metal or the like when the web is wound or unwound.
2. Description of the Related Art
Conventionally, as an apparatus for controlling the position of a web travelling along a given path when the web is unwound from a roll into which it has been wound, there is known an apparatus (which is disclosed in Japanese Patent Publication No. 54-30360) in which the edge of the web unwound is detected by use of an edge detector such as a photo-electric switch, a high-pressure air injection pipe or the like located at a predetermined position in a web travelling path, and the roll is moved in the axial direction thereof in accordance with signals produced by the edge detector so as to be able to maintain the position of the web edge in a predetermined range after the web is unwound.
Also, there is known another prior art apparatus (which is disclosed in Japanese Patent Publication No. 49-33726) in which the meandering of a web occurring when the web is wound into a roll can also be corrected by means of a technique similar to the above-mentioned one.
However, in the above-mentioned prior art edge position controlling apparatus, due to the fact that the roll is moved in the axial direction thereof in accordance with correction commands corresponding to the displacements of the position of the web edge regardless of the web travelling speed, when the web travelling speed becomes slower, over correction of the edge position of the web than necessary is carried out to produce "hunting" and, on the other hand, when the web travelling speed becomes faster, the edge position control may be delayed.